In HPLC, a sample to be examined needs to be injected into a high-pressure fluid flow, wherein this flow can be interrupted only as briefly as possible. For this purpose, high-pressure injection valves are used that allow a nearly uninterrupted change-over of the fluid flow. Such a design is described, for example, in U.S. Pat. No. 3,530,721. This patent was derived from an original application that was published in 1965.
U.S. Pat. No. 4,939,943 discloses a sample injector with a “high pressure syringe unit.” The basic Split Loop Principle of the sample injector disclosed in this application has proven effective in HPLC.
Furthermore, WO 2006/083776 discloses a sample injector for preventing pressure surges that occur during the actuation of the high-pressure valve and could negatively affect the efficiency and the service life of the chromatography column.
During the actuation of the injection valve, compression and decompression volumes flow through the valve with high speeds. According to non-previously-published German Patent Application DE 10 2007 059 651 A1 of the applicant of Dec. 10, 2007, which pertains to a sample injector for high performance liquid chromatography and features a high-pressure change-over valve with optimized service life, these flows cause damage to the high-pressure valve components.
The service life of the high-pressure change-over valve determines the operating costs of an HPLC system. These costs should be maintained as low as possible by minimizing the wear of the high-pressure valve components.